Many of you saw my pictures of the broken block published earlier on the brickboard. I removed the pistons from the block and did a little closer examining of the damage. First I must mention again that I found the hose connecting the turbo discharge fitting to the wastegate actuator broken. The wastegate was no longer functioning. Volvo engineers added another safety to prevent overboosting on LH 2.2 cars, and it is called the Charge Air Overpressure Switch. On 740Ts it is under the dashboard alongside the EZK unit. On 1988 model year and later 760Ts, it is mounted on the Coolant Reservoir as shown below.


The switch is pictured just as I found it, with the hose disconnected, probably accidently. The picture below shows broken connecting rod number three and bent connecting rod number two. When the 9mm connecting rods break from fatigue and manufacturing defects, they crack and then break at the big end around the tapped bolt holes. I also have two of those from another engine, and they don't look like these.


The picture below shows the broken piston in the block.


What I think happened is this: With the Wastegate Actuator and the Charge Overpressure Switch disconnected, whoever was driving this car was accelerating and didn't (and wouldn't have any reason to) notice the boost gauge needle turning clockwise until it was pointing at anywhere from 6 to 9 o'clock. The 9mm conecting rods just couldn't take it any more and two of them buckled. Number three broke obviously. I don't know if the piston broke first, or the connecting rod. The connecting rod could have become shortened enough for the piston to bottom out in the block or hit the crankshaft.

The Garrett T3 will easily produce this much boost. About six years ago my wife reported to me that the engine in her car was quitting. I went for a ride with her. The engine sure was quitting, it was quitting when the Charge Overpressure Switch hit it's limit of somewhere over 16 psi. Her car came with a Turbo+, and the overpressure switch does have a higher setting than stock. On her car the hose going to the Turbo+ solenoid had come off of the tee between the turbo outlet and the wastegate actuator.

Make sure the Wastegate Actuator and the Charge Overpressure Switch are connected!